reflex

reflex

[re´fleks]

a reflected action or movement; the sum total of any particular automatic response mediated by the nervous system. A reflex is built into the nervous system and does not need the intervention of conscious thought to take effect.

The knee jerk is an example of the simplest type of reflex. When the knee is tapped, the nerve that receives this stimulus sends an impulse to the spinal cord, where it is relayed to a motor nerve. This causes the quadriceps muscle at the front of the thigh to contract and jerk the leg up. This reflex, or simple reflex arc, involves only two nerves and one synapse. The leg begins to jerk up while the brain is just becoming aware of the tap.

Other simple reflexes, the stretch reflexes, help the body maintain its balance. Every time a muscle is stretched, it reacts with a reflex impulse to contract. As a person reaches or leans, the skeletal muscles tense and tighten, tending to hold him and keep him from falling. Even in standing still, the stretch reflexes in the skeletal muscles make many tiny adjustments to keep the body erect.

The “hot stove” reflex is more complex, calling into play many different muscles. Before the hand is pulled away, an impulse must go from the sensory nerve endings in the skin to a center in the spinal cord, from there to a motor center, and then out along the motor nerves to shoulder, arm, and hand muscles. Trunk and leg muscles respond to support the body in its sudden change of position, and the head and eyes turn to look at the cause of the injury. All this happens while the person is becoming aware of the burning sensation. A reflex that protects the body from injury, as this one does, is called a nociceptive reflex. Sneezing, coughing, and gagging are similar reflexes in response to foreign bodies in the nose and throat, and the wink reflex helps protect the eyes from injury.

A conditioned reflex is one acquired as the result of experience. When an action is done repeatedly the nervous system becomes familiar with the situation and learns to react automatically, and a new reflex is built into the system. Walking, running, and typewriting are examples of activities that require large numbers of complex muscle coordinations that have become automatic.

Nerve pathway of a simple reflex. When the sensory nerve ending is stimulated, a nerve impulse travels along a sensory (afferent) neuron to the spinal cord. Here an association neuron transfers the impulse to a motor (efferent) neuron. The motor neuron carries the impulse to a muscle, which contracts and moves a body part.

abdominal r's contractions of the abdominal muscles about the navel on stimulating the abdominal skin. It indicates that the spinal cord from the eighth to the twelfth thoracic nerve is intact.

cough reflex the sequence of events initiated by the sensitivity of the lining of the airways and mediated by the medulla as a consequence of impulses transmitted by the vagus nerve, resulting in coughing, i.e., the clearing of the passageways of foreign matter.

cremasteric reflex contraction of the ipsilateral cremaster muscle, drawing the testis upward, when the upper inner aspect of the thigh is stroked longitudinally.

deep reflex one elicited by a sharp tap on the appropriate tendon or muscle to induce brief stretch of the muscle.

Magnus and de Kleijn neck r's extension of both limbs on the same side, or one limb or part of a limb, with increase of tonus on the side to which the chin is turned when the head is rotated, and flexion with loss of tonus on the side to which the occiput points; it usually indicates decerebrate rigidity.

Mayer's reflex opposition and adduction of the thumb combined with flexion at the metacarpophalangeal joint and extension at the interphalangeal joint, on downward pressure of the index finger.

Mendel-Bekhterev reflex dorsal flexion of the second to fifth toes on percussion of the dorsum of the foot; in certain organic nervous disorders, plantar flexion occurs.

micturition reflex any of the reflexes necessary for effortless urination and subconscious maintenance of continence.

pilomotor reflex the production of goose flesh on stroking of the skin.

placing reflex flexion followed by extension of the leg when the infant is held erect and the dorsum of the foot is drawn along the under edge of a table top; it is obtainable in the normal infant up to the age of six weeks.

plantar reflex plantar flexion of the foot when the ankle is grasped firmly and the lateral border of the sole is stroked or scratched from the heel toward the toes.

proprioceptive reflex a reflex that is initiated by stimuli arising from some function of the reflex mechanism itself.

psychogalvanic reflex decreased electrical resistance of the body due to emotional or mental agitation.

pupillary reflex

1. contraction of the pupil on exposure of the retina to light.

2. any reflex involving the iris, resulting in change in the size of the pupil, occurring in response to various stimuli, e.g., change in illumination or point of fixation, sudden loud noise, or emotional stimulation.

stepping reflex movements of progression elicited when the infant is held upright and inclined forward with the soles of the feet touching a flat surface; it is obtainable in the normal infant up to the age of six weeks.

stretch reflex reflex contraction of a muscle in response to passive longitudinal stretching.

sucking reflex sucking movements of the lips of an infant elicited by touching the lips or the skin near the mouth.

suck-swallow reflex rhythmical sucking and swallowing movements in an infant when a finger or nipple is placed in the mouth.

superficial reflex any withdrawal reflex elicited by noxious or tactile stimulation of the skin, cornea, or mucous membrane, including the corneal, pharyngeal, and cremasteric reflexes.

tendon reflex contraction of a muscle caused by percussion of its tendon.

tonic neck reflex extension of the upper limb and sometimes the lower limb on the side to which the head is forcibly turned, with flexion of the contralateral limbs; seen normally in the newborn. If it persists into the second or third year of life, it indicates a neurologic disorder.

triceps reflex contraction of the belly of the triceps muscle and slight extension of the upper limb when the tendon of the muscle is tapped directly, with the limb flexed and fully supported and relaxed.

vestibular r's the reflexes for maintaining the position of the eyes and body in relation to changes in orientation of the head.

vestibulo-ocular reflex nystagmus or deviation of the eyes in response to stimulation of the vestibular system by angular acceleration or deceleration or when the caloric test is performed.

vomiting reflex the reflex for vomiting, caused by reflexive stimulation of muscles of the gastrointestinal tract and throat; it is mediated by centers in the medulla oblongata and can be set in motion by a variety of stimuli. See also gag reflex.

re·flex

(rē'fleks), Do not confuse this word with reflux.

1. An involuntary reaction in response to a stimulus applied to the periphery, and transmitted to the nervous centers in the brain or spinal cord. Most deep reflexes are stretch or myotatic reflexes, elicited by striking a tendon or bone, causing stretching, even slight, of the muscle, which then contracts as a result of the stimulus applied to its proprioceptors. See also: phenomenon.

2. A reflection.

[L. reflexus, pp. of reflecto, to bend back]

reflex

/re·flex/ (re´fleks) a reflected action or movement; the sum total of any particular automatic response mediated by the nervous system.

abdominal reflexes contractions of the abdominal muscles on stimulation of the abdominal skin.

accommodation reflex the coordinated changes that occur when the eye adapts itself to near vision; constriction of the pupil, convergence of the eyes, and increased convexity of the lens.

3. a spot of light seen reflected from the retina with the retinoscopic mirror.

Magnus and de Kleijn neck reflexes extension of both ipsilateral limbs, or one, or part of a limb, increase of tonus on the side to which the chin is turned when the head is rotated to the side, and flexion with loss of tonus on the side to which the occiput points; sign of decerebrate rigidity except in infants.

Mendel-Bekhterev reflex dorsal flexion of the second to fifth toes on percussion of the dorsum of the foot; in certain organic nervous disorders, plantar flexion occurs.

micturition reflex any of the reflexes necessary for effortless urination and subconscious maintenance of continence.

Moro's reflex flexion of an infant's thighs and knees, fanning and then clenching of fingers, with arms first thrown outward and then brought together as though embracing something; produced by a sudden stimulus and seen normally in the newborn.

neck reflexes reflex adjustments in trunk posture and limb position caused by stimulation of proprioceptors in the neck joints and muscles when the head is turned, tending to maintain a constant orientation between the head and body.

neck righting reflex rotation of the trunk in the direction in which the head of the supine infant is turned; this reflex is absent or decreased in infants with spasticity.

nociceptive reflexes reflexes initiated by painful stimuli.

oculocardiac reflex a slowing of the rhythm of the heart following compression of the eyes; slowing of from 5 to 13 beats per minute is normal.

open loop reflex a reflex in which the stimulus causes activity that it does not further control and from which it does not receive feedback.

Oppenheim reflex dorsiflexion of the big toe on stroking downward along the medial side of the tibia, seen in pyramidal tract disease.

orbicularis oculi reflex normal contraction of the orbicularis oculi muscle, with resultant closing of the eye, on percussion at the outer aspect of the supraorbital ridge, over the glabella, or around the margin of the orbit.

orbicularis pupillary reflex unilateral contraction of the pupil followed by dilatation after closure or attempted closure of eyelids that are forcibly held apart.

patellar reflex contraction of the quadriceps and extension of the leg when the patellar ligament is tapped.

peristaltic reflex when a portion of the intestine is distended or irritated, the area just proximal contracts and the area just distal relaxes.

pharyngeal reflex contraction of the pharyngeal constrictor muscle elicited by touching the back of the pharynx.

pilomotor reflex the production of goose flesh on stroking the skin.

placing reflex flexion followed by extension of the leg when the infant is held erect and the dorsum of the foot is drawn along the under edge of a table top; it is obtainable in the normal infant up to the age of six weeks.

plantar reflex irritation of the sole contracts the toes.

proprioceptive reflex one initiated by a stimulus to a proprioceptor.

pupillary reflex

1. contraction of the pupil on exposure of the retina to light.

2. any reflex involving the iris, resulting in change in the size of the pupil, occurring in response to various stimuli, e.g., change in illumination or point of fixation, sudden loud noise, or emotional stimulation.

tendon reflex one elicited by a sharp tap on the appropriate tendon or muscle to induce brief stretch of the muscle, followed by contraction.

tonic neck reflex extensions of the arm and sometimes of the leg on the side to which the head is forcibly turned, with flexion of the contralateral limbs; seen normally in the newborn.

triceps reflex contraction of the belly of the triceps muscle and slight extension of the arm when the tendon of the muscle is tapped directly, with the arm flexed and fully supported and relaxed.

triceps surae reflex plantar flexion caused by a twitchlike contraction of the triceps surae muscle, elicited by a tap on the Achilles tendon, preferably while the patient kneels on a bed or chair, the feet hanging free over the edge.

Triceps surae reflex.

vestibular reflexes the reflexes for maintaining the position of the eyes and body in relation to changes in orientation of the head.

vestibuloocular reflex nystagmus or deviation of the eyes in response to stimulation of the vestibular system by angular acceleration or deceleration or when the caloric test is performed.

withdrawal reflex a nociceptive reflex in which a body part is quickly moved away from a painful stimulus.

reflex

(rē′flĕks′)

adj.

1. Physiology Being an involuntary action or response, such as a sneeze, blink, or hiccup.

2. Bent, turned, or thrown back; reflected.

3. Reflexed.

n.

1.

a. Physiology An involuntary response to a stimulus.

b. reflexes A person's ability to respond to new or changing stimuli: His quick reflexes make him a good taxi driver.

2. Psychology An unlearned or instinctive response to a stimulus.

reflex

[rē′fleks]

Etymology: L, reflectere, to bend back

1 a backward or return flow of energy or of an image, as a reflection.

Reflex

reflex

rapid innate response by an effector (muscle or gland) to a stimulus detected by neural receptors and signalled by afferent nerves to neurons in the central nervous system whose efferent nerves activate the effector. reflex arc this neural pathway, including one or more synaptic connections. See alsostretch reflex, tendon reflex (tendon jerk).

reflex,

n an automatic, predictable and adaptive neuromuscular response to a stimuli.

reflex

1. Involuntary response to a stimulus.

2. Reflection or an image formed by reflection (e.g. corneal reflex).accommodative reflexSeereflex accommodation; near reflex.reflex arcSeepupil light reflex.blinking reflex Blinking in response to various stimulations such as a light source or a mechanical threat. Seeretinotectal pathway.cat's eye reflex A whitish, bright reflection observed in the normally black pupil in several conditions, such as leukocoria, retinoblastoma, Coats' disease or persistent hyperplastic primary vitreous. It resembles the reflection from the tapetum lucidum of a cat when a light is shined at night.consensual light reflexSeepupil light reflex.corneal reflex1. Blinking in response to a threat, or to tactile stimulation of the cornea, as for example when measuring objectively the corneal touch threshold. Associated responses include lacrimation and miosis. 2. Image formed by reflection of light from the cornea (Fig. R5). Seeaesthesiometer; Hirschberg's method; Krimsky's method; pupillometer; apparent strabismus.direct light reflexSeepupil light reflex.eyeball compression reflexSeeoculocardiac reflex.fixation reflex Psycho-optical reflex consisting of an involuntary movement of the eye (or eyes) aimed at placing on the foveola the retinal image of an object that was formed in the retinal periphery. Seepsycho-optical reflex; re-fixation reflex.foveal reflex Tiny reflection from the concave surface of the foveal depression of the retina seen in ophthalmoscopy. It is not usually visible in old eyes.fundus reflex Light reflected by the fundus of the eye, as seen in retinoscopy and ophthalmoscopy. It appears as a red glow in the plane of the pupil in retinoscopy. It is absent when the eye has a dense cataract. Syn. red reflex.fusion reflexSeemotor fusion.hemianopic pupillary reflex In hemianopia, a loss of pupillary constriction when light falls on the blind side of the retina while pupillary constriction is maintained when light stimulates the unaffected side of the retina. Syn. Wernicke's hemianopic pupil; Wernicke's pupillary reaction; Wernicke's pupillary reflex; Wernicke's sign.indirect light reflexSeepupil light reflex.lacrimal reflex Secretion of tears in response to irritation of the cornea or conjunctiva as, for example, when first wearing contact lenses (hard in particular), but it may also be induced by eyestrain, glare, laughing, etc. Syn. lacrimation reflex; tearing reflex; weeping reflex. Seelacrimal apparatus; tear secretion; Schirmer's test.lacrimation reflexSeelacrimal reflex.light reflex1. That light which appears in the pupil in retinoscopy. It is light reflected by the retina. Syn. retinoscopic light. 2. Any reflected light. Seepupil light reflex.near reflex Reflex evoked by a blurred retinal image, as when fixating from far to near. It consists of three responses: (1) increased convexity of the crystalline lens; (2) constriction of the pupils; and (3) convergence of the eyes. This reflex is not a pure reflex since each of the three components can act independently of the other two; convergence by means of prisms, accommodation by means of lenses and miosis by light stimulation. Syn. accommodative reflex; near-triad reflex; synkinetic near reflex. Seemechanism of accommodation; reflex accommodation; accommodative response.near-triad reflexSeenear reflex.oculocardiac reflex A decrease in pulse rate following compression of the eyeball or traction on the extraocular muscles during ocular surgery. It may produce a systolic cardiac arrest. Syn. Ascher's phenomenon; Ascher's reflex; eyeball compression reflex.optokinetic reflexSeevestibulo-ocular reflex.postural reflex A reflex which helps to maintain static or dynamic posture of the body, for example, the righting reflex, in which visual stimuli help to maintain a correct position of the head in space by activating the muscles of the neck and limbs. Seestatic eye reflex.psycho-optical reflex Reflexes involving the eye which are mediated by the occipital cortex such as the accommodative, fixation, fusion, version and vergence reflexes.pupil reflex Any alteration of the pupil size in response to stimuli other than light (e.g. a sudden noise). Seepupil light reflex.pupil light reflex1. Constriction of the pupil in response to light stimulation of the retina. The response of an eye to light stimulation can occur either with a light shining on it directly (the direct light reflex) or when the other eye is stimulated (the consensual or indirect light reflex). The reflex arc consists of four neurons beyond the ganglion cells. The first afferent neuron transmits nervous impulses from the retina to the two pretectal olivary nuclei, located on the lateral and anterior side of the super-ior colliculi, in response to light stimulation of the photoreceptors. The second neurons, called the internuncial neurons, connect each pretectal olivary nucleus to both Edinger-Westphal nuclei which form part of the oculomotor nuclei. The third efferent neurons connect the latter nuclei, via the third nerve (oculomotor nerve) to the ciliary ganglion where there is a synapse. The fourth efferent neurons connect the latter, via the short ciliary nerves, to the sphincter pupillae muscle of each iris and constrict the pupil. Light stimulation of the central region of the retina produces a greater pupillary response than peripheral stimulation. The efferent path for pupil constriction represents the parasympathetic innervation (Fig. R6). Note: recent research points to a different pathway for the second afferent neuron: almost all of the fibres from each pretectal olivary nucleus project to the contralateral Edinger-Westphal nucleus. 2. Dilatation of the pupil in response to a reduction of the light stimulation of the retina. It is effected by sympathetic innervation, which originates in the hypothalamus and descends down the brainstem to the ciliospinal centre (of Bulge), located between C8 and T2. From there fibres pass to the superior cervical ganglion in the neck, then efferent fibres ascend along the internal carotid artery until they join the ophthalmic division of the trigeminal nerve. The fibres reach the dilator pupillae muscle of the iris via the nasociliary and long ciliary nerves, which enter the eyeball behind the equator. Syn. light reflex. Seepupillary fibres; retinotectal pathway; pretectum; efferent pupillary defect.red reflexSeefundus reflex.re-fixation reflex This reflex occurs while fixating one object and another in the visual field attracts the attention. The eye then turns to fixate on the new object. This is a special case of the fixation reflex.retinoscopic reflexSeelight reflex; retinoscope.righting reflexSeepostural reflex.static eye reflex A higher order postural reflex which helps to maintain the eye static with respect to the visual environment by action on the extraocular muscles (possibly via the utricular receptors of the vestibular system) during head or body movements. Syn. compensatory eye movements.reflex tearingSeelacrimal reflex.tonic neck reflex Orientation of the head, eyes and body in response to proprioceptive information provided by the activity of the muscles of the neck. Seeproprioception.vergence reflex A disjunctive fixation reflex in response to an object that moves closer or further than the original position of the fixation point. Seedisjunctive eye movements.version reflex A conjugate fixation reflex in response to an object moving in the same frontal plane. Seeversion.vestibulo-ocular reflex A conjugate movement of the eyes in the direction opposite to a head movement. This reflex is triggered by stimulation of the semicircular canals. It is aimed at maintaining a stable image on the retina during head movement. This reflex responds best at high velocities and frequencies of the visual stimulus. At low velocities and frequencies the stabilization of the ret-inal image is attempted by the optokinetic reflex, which is triggered only by retinal stimulation: this latter reflex complements the vestibulo-ocular reflex. Seenystagmus; optokinetic.weeping reflexSeelacrimal reflex.Wernicke's pupillary reflexSeehemianopic pupillary reflex.white pupillary reflexSeeleukocoria.

Fig. R5 Frontal view of the right eye

Fig. R6A, pupils under low illumination

re·flex

(rē'fleks)

Involuntary reaction to a stimulus applied to periphery and transmitted to nervous centers in brain or spinal cord.

[L. reflexus, pp. of reflecto, to bend back]

reflex(es) (rē´fleks),

n a reflected action or movement; the sum total of any specific involuntary activity.

n gagging or vomiting induced by touching the mucous membrane of the throat or as a result of other noxious stimuli. Also called gag reflex.

reflex, Hering-Breuer

n.pr the nervous mechanism that tends to limit the respiratory excursions. Stimuli from the sensory endings in the lungs (and perhaps in other parts) pass up the vagi and tend to limit both inspiration and expiration during ordinary breathing.

reflex, jaw,

n an extension-flexion reflex that is initiated by tapping the mandible downward. The masseter and other elevators of the mandible are the first stretched; then the reflex flexion-contraction elevates the mandible by flexion of elevator muscles while simultaneous stretching (extension) of the depressor muscles of the mandible occurs.

reflex, pharyngeal

n contraction of the constrictor muscles of the pharynx, elicited by touching the back of the pharynx.

reflex, stretch,

n one of the most important features of tonic contraction of muscle. It is the reflex contraction of a healthy muscle that results from a pull. It has been found that stretching a muscle by as little as 0.8% of its original length is sufficient to evoke a reflex response. A stretch of constant degree causes a maintained steady contraction, muscle spindles and stretch receptors in the tendons show very slow adaptation, and the reflex ceases immediately on withdrawal of the stretching force. The stretch reflex is obtained predominantly from those muscles maintaining body posture, among which are the masticating muscles that maintain the position of the mandible and the neck muscles holding the head erect. Together the masticating muscles and neck muscles are responsible for the maintenance of the air and food passages.

reflex, vagovagal

n a reflex in which the afferent and efferent impulses travel via the vagus nerve. The afferent impulses travel centrally via the sensory nucleus of the vagus. The efferent impulses travel via the motor fibers of the vagus nerve.

reflexes, allied,

n.pl reflexes that join to effect a common purpose, such as mastication. They may arise from diverse stimuli, such as smell, taste of food, and texture, shape, and resistance of the food bolus. Collectively, they encourage salivation and a sequence of masticatory closures of the mandible, followed by deglutition.

reflexes, antagonistic,

n.pl reflexes that cannot occupy the final pathway simultaneously. The weaker of these reflexes will give way to the stronger, especially if the latter is a protected reflex (e.g., a hot or nauseating food causes involuntary retching or even vomiting rather than the pleasurable gustatory experience associated with chewing and swallowing tasty food).

reflexes, flexion-extension,

n.pl the reflexes based on the principle of reciprocal innervation. When a voluntary or reflex contraction of a mus-cle occurs, it is accompanied by the simultaneous relaxation of its antagonist. E.g., when the jaw reflex is ini-tiated by tapping the mandible downward, the masseter and other elevators of the mandible are stretched. Then, reflex flexion-contraction of the ele-vators takes place, the mandible is elevated, and the depressor muscles of the mandible are stretched. Many combinations exist, not only between the agonists and the antagonists of a given joint but also between reflexes that cross over to muscle groups of contralateral extremities, joints, and muscles.

reflexes, pathologic,

n.pl reflexes observed in the abnormal or inappropriate motor responses of controlled stimuli initiated in the sensory organ that is appropriate to the reflex arc. They may be initiated in the superficial reflexes of the skin and mucous membrane; in the deep myotatic reflexes of the joints, tendons, and muscles; and in the visceral reflexes of the viscera and other organs of the body. The pathologic reflexes are thus syndromes of abnormal responses to otherwise normal stimuli.

reflex

a reflected involuntary action or movement; the sum total of any particular automatic response mediated by the nervous system.

A reflex is built into the nervous system and does not need the intervention of conscious thought to take effect.

relaxation of the anal sphincter which occurs with distention of the rectum and during defecation.

stepping reflex

movements of progression elicited when the animal is held upright and inclined forward with the feet touching a flat surface.

stretch reflex

reflex contraction of a muscle in response to passive longitudinal stretching.

superficial reflex

any withdrawal reflex elicited by noxious or tactile stimulation of the skin, cornea or mucous membrane, including the corneal and pharyngeal reflexes.

tapetal reflex

tapetal reflection of light.

tendon reflex

a method of testing the patency of reflex arc. The tendon is stretched sharply by tapping it close to its insertion. A positive reaction is a sharp contraction of the muscle of which the tendon is part. The patellar reflex is the best known of these reflexes. Absence indicates a defect in the reflex arc, an exaggerated response suggests an upper motor neuron lesion. Called also myotactic reflex.

a test of the ophthalmic and mandibular divisions of the trigeminal nerve, and the abducens nerve. Light touching of the cornea should result in retraction of the globe and protrusion of the nictitating membrane.

reflex walking

spinal reflexes can provide support and uncoordinated use of the hindlegs that resembles walking, in dogs with transection of the spinal cord between T13 and L4.

whisker reflex

pinching the pinna elicits a twitch of the whiskers in cats; used in assessment of depth of anesthesia.

Patient discussion about reflex

A. Ok I would like to ask if any others with RSD would like to get to know each other it looks like they have groups ,no one without RSD can appreciate the pain and the way those who you love the most ,think you are a faker because some RSDers ,you can't see anything readily ,not being believed with Nerve pain thayt is worse than anything I have felt like being shot ,blown up ,Third Degree Burns well kinda like when the nerves stgart to grow back from Third degree burns but 24/7 and the same degree of p[ain since 1968 .IF RSD IS CAUGHT IN THE FIIRST YEAR IT CAN BE Reversed so yes I want knowledge (oops didnt mean caps(to yell)Thank You rsdno

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